A respirator product in the form of a gas mask with port openings for filters as well as with an inspiration valve and with an expiration valve is known from DE 40 17 336 C1. Respirator filters can be arranged at different points of the half mask by means of a port adapter that can be fastened to a half mask in two preferential positions. The gas flow over the respirator filter is guided into the interior space of the mask to the mask user by means of directional valves, which are arranged both in the area of the respirator filter and at the gas outlet of the gas mask, and the breathing mask enters the environment via an expiration valve during the expiration phase. The directional valves comprise a valve seat and a valve membrane lying on the valve seat, which is fastened centrally at the valve seat. The valve membrane is lifted off from the valve seat during gas flow through the directional valve, so that a gas flow is made possible. The drawback of the prior-art valve design is that the flow resistance is relatively high, because the length of the membrane section that can be deflected by the gas flow is limited by the diameter of the valve seat due to the valve membrane being fastened centrally.
Directional valves for breathing masks that have a valve membrane that is fastened at the valve seat on one side and can be lifted off from the valve seat in the manner of a flap are known. Such a directional valve is described, for example, in U.S. Pat. No. 6,047,698. A valve membrane cut to a rectangular shape lies on a flat valve seat and is pressed against the valve seat by a fixing lug fastened to the edge of the valve cover. Even though a markedly lower flow resistance can be achieved with this valve design than with a directional valve with centrally fastened valve membrane, leakage is higher because of the one-sided fastening of the valve membrane, and the valve membrane may stick due to the adhesive forces in case of a possible condensation of moist expired air on the inside of the valve cover, as a result of which the closing of the directional valve may be delayed or may fail to occur altogether.